Fatal error: Uncaught TypeError: Argument 1 passed to iterator_to_array() must implement interface Traversable, null given in /opt/lampp/htdocs/vendor/magento/framework/View/Element/Html/Calendar.php:86 Stack trace: #0 /opt/lampp/htdocs/vendor/magento/framework/View/Element/Html/Calendar.php(86): iterator_to_array(NULL) #1 /opt/lampp/htdocs/vendor/magento/framework/View/Element/AbstractBlock.php(659): Magento\Framework\View\Element\Html\Calendar->_toHtml() #2 /opt/lampp/htdocs/vendor/magento/framework/View/Layout.php(542): Magento\Framework\View\Element\AbstractBlock->toHtml() #3 /opt/lampp/htdocs/vendor/magento/framework/View/Layout.php(518): Magento\Framework\View\Layout->_renderBlock('html_calendar') #4 /opt/lampp/htdocs/var/generation/Magento/Framework/View/Layout/Interceptor.php(206): Magento\Framework\View\Layout->renderNonCachedElement('html_calendar') #5 /opt/lampp/htdocs/vendor/magento/framework/View/Layout.php(472): Magento\Framework\View\Layout\Interceptor->renderNonCachedElement('html_calendar') #6 /opt/lampp/ in /opt/lampp/htdocs/vendor/magento/framework/View/Element/Html/Calendar.php on line 86